What is the third character?

Of all the annoyances of the modern world, nothing is more maddening than these so-called "captcha" codes. Half the time they are unreadable. Often it is not even possible to type in the undecipherable symbols presented. And most infuriating of all is when you have thoughtfully typed your entire complaint or comment, then mistype the captcha only to see your entire text disappear. Who is the idiot who created this absurd process for detecting non-humans and why do so many companies subscribe to it when it is sure to make their customers detest them?